Two-thirds of people who catch Covid-19 are still infectious five days after their symptoms begin, research has suggested.
The findings, from a study by Imperial College London, potentially have serious ramifications for how long employers should be asking employees to isolate following a positive diagnosis, especially as many have now scrapped needing to isolate altogether.
Current NHS guidance suggests people should try to stay at home following a positive test and avoid contact with others for five days.
However, it is no longer a legal requirement to self-isolate if you test positive. Many employers are as a result now requiring employees to come into work, even if they have had a positive test, as long as they are not feeling unwell.
The research, published in journal The Lancet Respiratory Medicine, has been billed as the first to unveil how long infectiousness lasts for after natural Covid-19 infection in the community.
The study team conducted detailed daily tests from when people were exposed to SARS-CoV-2 to look at how much infectious virus they were shedding.
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The findings suggested that, in people who develop symptoms, the majority are not infectious before symptoms develop. However, two-thirds of cases are still infectious five days after their symptoms begin.
The study also suggested that, while lateral flow tests do not detect the start of infectiousness well, they more accurately identify when someone is no longer infectious and can safely leave isolation.
Study author Professor Ajit Lalvani, director of the NIHR Respiratory Infections Health Protection Research Unit at Imperial, said: “We closely monitored people in their homes from when they were first exposed to the virus, capturing the moment when they developed infection through until they ceased being infectious.
“Before this study we were missing half of the picture about infectiousness, because it’s hard to know when people are first exposed to SARS-CoV-2 and when they first become infectious.
“By using special daily tests to measure infectious virus (not just PCR) and daily symptom records we were able to define the window in which people are infectious. This is fundamental to controlling any pandemic and has not been previously defined for any respiratory infection in the community,” he added.
The research follows a study from the Cedars-Sinai Medical Centre in the US that concluded most people who were infected with the omicron variant of Covid-19 did not even realise they were ill.
Autumn booster vaccine plans
Separately, NHS England has outlined its plans for the next vaccine rollout programme, which will start from next month.
Bookings for the new ‘bivalent’ Covid vaccine (meaning it will target both omicron and the original 2020 virus) will open from the week of 5 September, with care home residents and those who are housebound prioritised first.
The programme will then pick up pace from the following week, starting 12 September, with the NHS inviting those most susceptible to serious illness from Covid-19 and those aged 75 and over to book an appointment.
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In all, around 26 million people across England will be eligible for an autumn booster in line with guidance set out by the Joint Committee on Vaccination, including all over-50s.
As many as 3,000 sites are expected to be part of the rollout, including GP practices and community pharmacies, NHS England has said.
